Through-Hole Assembly

Through-hole technology is the mounting process by which component leads are placed into the drilled hole of a bare printed circuit board and soldered to the pads on the opposite side. This can be achieved with either manual assembly or automated insertion mount machines. Through-hole mounting was the standard practice until surface mount technology (SMT) debuted in the 1980s. Through-hole technology was popular in the construction of second-generation computers in the 1950s. Over time, PCBs moved from one-sided to two-sided boards, then graduated to multi-layer boards.

The advent of surface mount technology was initially thought to have made through-hole technology obsolete. However, through-hole technology proved to have staying power because of its unique advantages and reliability.

Through-hole components have proven to be more dependable when it comes to products that require stronger connections between layers. The through-hole component leads can withstand a lot more environmental stress because they run through the board, as compared to SMT components that are only secured by the solder on the board’s surface. This distinct advantage makes through-hole technology the preferred process for aerospace and military products that endure extremes in temperature, acceleration, and force.

Through-hole is also the preferred method for applications that require testing and prototyping because it allows for manual replacement and adjustment. Through-hole technology is more expensive than SMT because of its strong mechanical bonds. This is why through-hole technology is reserved mostly for heavier, bulkier components such as semiconductors in large packages or electrolytic capacitors. The technology is also popular for components that require great strength in support, such as electromechanical relays or connectors.

Many design engineers and manufacturers prefer the reliable through-hole technology to SMT in prototyping because it allows the use of breadboard sockets.